OK, Jed, this is a nit, and I'm stating that up front. But with that said...
On 04/20/2011 02:08 PM, Jed Rothwell wrote: > > There is no need to measure the pump input because it cannot transfer > to the system between the inlet and outlet temperature sensors. The > water does not slow down or stop between those points, so none of the > pump energy converts to heat. The heat added to the water by the pump > mechanical action is added before the inlet sensor, so it does not > register. Say WHAT? You just "proved" that all pipes inside the ecat are *frictionless* !! Because the water flow doesn't slow, you assert that no energy from the flowing water can have been lost to heat -- that's absurd! It cannot be true for any physical pipe carrying physical water (if this were liquid helium the story might be different). In fact, what you would find if you could take *extremely* precise pressure measurements all along the pipe, is that the pressure of the water DROPS, very gradually, as you move along the pipe away from the pump. It is this (very slight) pressure gradient which drives the water through the pipe against the force of friction. Flow rate, on the other hand, is (obviously) constant along the pipe (unless there's a leak). This is very similar to the situation in electronics, where there's a "voltage drop" along wires carrying current. In practice the friction between the water and the pipe is so small that heating effects from it can be ignored, and most of the time the attendant pressure drop is also ignorable. If the passages inside the eCat were truly labyrinthine, and anyone cared to measure the pressure before and after the eCAT, you'd most likely find that there was, indeed, a macroscopic pressure drop. But if it's a simple flow-through configuration you'd have a very hard time detecting the drop.
